Intervertebral disc prosthesis

ABSTRACT

This disclosure relates to intervertebral disc prostheses which may have an upper plate, a lower plate, and a mobile core, with the upper surface of the core being in contact with at least a part of the lower surface of the upper plate. In some configurations, limit stops reduce friction while limiting or preventing the movements of the core relative to the lower plate, in translation and in rotation, respectively, along an axis substantially parallel to the lower plate and about an axis substantially perpendicular to the lower plate. Instrumentation for insertion of the prostheses into intervertebral spaces is also described.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/513,818 filed Oct. 14, 2014, and issuing as U.S. Pat. No. 9,655,739on May 23, 2017, which is a continuation of U.S. patent application Ser.No. 11/051,710 filed Feb. 4, 2005, and issuing as U.S. Pat. No.8,858,635 on Oct. 14, 2014, which claims priority under 35 U.S.C. §119to French Patent Application No. 0401024 filed in FRANCE on Feb. 4,2004.

TECHNICAL FIELD

The present invention relates to intervertebral disc prostheses.

BACKGROUND

Various types of prostheses are known in the prior art. Numerousprostheses are constituted by a lower plate and an upper plate enclosinga central core. A part of these prostheses enables the upper plate toslide relative to the central core and optionally permits the centralcore to slide relative to the lower plate. This sliding of the centralcore relative to the lower plate allows spontaneous positioning of thecore in the ideal position to absorb constraints imposed on theprosthesis during movements made by the patient carrying the prosthesis.However, because of the forces from applied constraints, materialsutilized and the form of the different pieces constituting theprosthesis, the sliding of the core is often difficult, which causesrapid wear and heightens the risk of ejection of at least a part of theprosthesis to the outside of the spine, and this is not desirable forthe patient.

An intervertebral disc prosthesis is provided that allows movement ofthe different pieces of the prosthesis between one another, butfacilitates core sliding.

Intervertebral disc prostheses in accordance with the present inventioncomprise at least three pieces including a first plate, a second plateand a core that is mobile relative to at least one of the plates. In apreferred embodiment, the core has a curved surface in contact with atleast a part of a complementary curved surface of the first plate and asubstantially flat surface in contact with at least a part of asubstantially flat surface of the second plate, and limit stops situatednear the periphery of the second plate and of the core that limit orprevent, without excessive friction, the movements in translation of thecore relative to the second plate, along an axis substantially parallelto the substantially flat surfaces, and limit or prevent the movementsin rotation of the core relative to the second plate, about an axissubstantially perpendicular to the substantially flat surfaces. In apreferred embodiment, the substantially flat surface of the core has atleast one dummy hole facilitating sliding of the core relative to thesubstantially flat surface of the second plate with which it is incontact.

According to another particular feature in an embodiment, the lowersurface of the core and the upper surface of the second plate, known asthe lower plate, are substantially flat.

According to another particular feature in an embodiment, at least thesubstantially flat surface of the core is enclosed in a protectiveshell, whereof the surface in contact with the substantially flatsurface of the second plate and with the substantially flat of the corehas at least one hole.

According to another particular feature in an embodiment, the protectiveshell of the core does not cover the limit stops of the core, so as toavoid contact of the protective shell with the limit stop of the secondplate.

According to another particular feature in an embodiment, the area ofcontact of the substantially flat surface of the core or of theprotective shell with the substantially flat surface of the second plateand the area of contact of the curved surface of the core with thecurved surfaces of the first plate are substantially equal, on bothsides of the core.

According to another particular feature in an embodiment, the angleformed by the edges of the hole present at least on the substantiallyflat surface of the core or of the protective shell of the core issoftened to improve the sliding of the core or of the shell on thesubstantially flat surface of the second plate.

According to another particular feature in an embodiment, the holepresent on the substantially flat surface of the core or of theprotective shell of the core is prolonged, as far as the periphery ofthis substantially flat surface, by grooves forming channels via whichthe interstitial liquid from surrounding tissue can play a lubricatingrole to improve the sliding of the core on the substantially flatsurface of the second plate, when the prosthesis is in place on thepatient.

According to another particular feature in an embodiment, the angleformed by the edges of the grooves prolonging the hole as far as theperiphery of the substantially flat surface of the core or of theprotective shell of the core is softened to improve the sliding of thecore or of the shell on the substantially flat surface of the secondplate.

According to another particular feature in an embodiment, the core ismade of polyethylene.

According to another particular feature in an embodiment, the protectiveshell of the core is made of metal.

According to another particular feature in an embodiment, the first andsecond plates are made of metal.

According to another particular feature in an embodiment, the limitstops consist of male structure of the second plate, cooperating withfemale structure of the core.

According to another particular feature in an embodiment, the core ismobile relative to the first and/or second plates and that a variableangle between the first and second plates depends on the position of thecore, an inclination, in any direction at all, of at least the firstplate inducing the displacement of the core between the plates andproviding freedom of movement for the patient and, at the same time,helping eliminate the positioning defects of the prosthesis.

According to another particular feature in an embodiment, an anglebetween the upper surface of the upper plate and the lower surface ofthe lower plate can be imposed either by the fact that the plane meansrepresenting the upper and lower surfaces of the core form an angle, orby the fact that the plane means representing the upper and lowersurfaces of the first plate and/or of the second plate form an angle, orby restriction of the movements of the core about a position imposinginclination of at least the first plate.

According to another particular feature in an embodiment, the sameplates can be assembled with cores of different thicknesses.

According to another particular feature in the embodiment, at least apart of the surface of the first plate is concave and complementary tothe surface of the core with which it is in contact.

According to another particular feature in the embodiment, thedimensions of each male structure are slightly less than those of eachfemale structure so as to permit slight clearance between the core andthe second plate.

According to another particular feature in the embodiment, thedimensions of each male structure are substantially the same as those ofeach female structure so as to prevent any clearance between the coreand the second plate.

According to another particular feature in the embodiment, the malestructure of the second plate are two contact plates situated oppositeone another on two edges of the prosthesis, and the female structure ofthe core are two recesses.

According to another particular feature in the embodiment, the malestructure of the second plate are two walls situated opposite oneanother in the vicinity of two edges of the prosthesis, and in that thefemale structure of the core are recesses.

According to another particular feature in the embodiment, the malestructure of the lower plate are two nibs curved towards the interior ofthe prosthesis and situated opposite one another on two edges of theprosthesis, and the female structure of the core are two recesses.

According to another particular feature in the embodiment, at least oneof the nibs is replaced by a pin equipped with a hole and on which aplate is fixed by means of a dowel penetrating the hole.

According to another particular feature in the embodiment, the lowersurface of the lower plate and the upper surface of the upper plate areprovided with teeth or notches situated in the vicinity of at least twoedges of the prosthesis and oriented so as to prevent sliding of theprosthesis prior to its adhesion to the osseous tissue permitted by aporous biocompatible coating of the surfaces of the plates in contactwith the vertebrae.

According to another particular feature in the embodiment, at least thesecond plate comprises one or more openings in the vicinity of its frontside, provided to receive anchoring means of the prosthesis in avertebra.

According to another particular feature in the embodiment, the openingsof the second plate are circular, and in that the anchoring means havethe form of a stud.

According to another particular feature in the embodiment, the head ofthe anchoring means have larger dimensions than the openings of thesecond plate, the anchoring means being fixed into a vertebra, thesecond plate is sandwiched in between the head of the anchoring meansand said vertebra.

According to another particular feature in the embodiment, the upperplate is bulged on at least a part of its upper surface to adapt to theform of the vertebrae.

Another aim is to propose an insertion device, between two vertebrae, ofintervertebral disc prostheses constituted by a lower plate, an upperplate and a mobile core at least relative to the lower plate. It wouldbe advantageous for the prosthesis insertion device between twovertebrae to allow the prosthesis to be kept sterile, to position itfacing the opening made by the surgeon between the two vertebrae, tohave it enter this opening by translation then to withdraw the deviceleaving the prosthesis inserted in its opening.

This aim is attained by an insertion device, between two vertebrae, ofintervertebral disc prostheses constituted by a first plate, an secondplate and a mobile core at least relative to the second plate,characterised in that it comprises a clip whereof the front surface hasa form provided to fit the form of the front edge of the prosthesis andwhereof at least two edges are equipped with a gripping means.

According to another particular feature in the embodiment, the grippingmeans present on the clip may be exhibited, for example, as two flexibleblades mounted on the lateral edges of the clip and holding theprosthesis by pinching the lateral edges of the upper and lower platesof the prosthesis.

According to another particular feature in the embodiment, the frontsurface of the clip has a form provided to fit the form of the frontedge of the prosthesis, on one hand, owing to its height at leastsubstantially equal to the height of the prosthesis, so as to come intocontact with the front edges of each of the plates of the prosthesisand, on the other hand, to at least one groove in at least the medianpart of the front surface of the clip to likewise come in contact withthe front edge of the core which is slightly set back relative to thefront edges of the plates.

According to another particular feature in the embodiment, the rearsurface of the clip can be pushed by a first end of a rod, known as aguide, equipped with a pusher at its other end and with a limit stop ata variable position along the guide for limiting the length of thesliding of the guide inside a body of a charger equipped with a head inwhich is arranged a space dimensioned for receiving the prosthesis andthe clip, the position of the limit stop on the guide being adjustablesuch that the prosthesis, held by the clip, exits from the head of thecharger and is centred relative to the vertical axis of the twovertebrae between which it must be implanted when the limit stopcontacts the body of the charger.

According to another particular feature in the embodiment, the front endof the gripping means of the prosthesis present on at least two edges ofthe clip is larger than their back end at which the width of the clip issubstantially equal to the width of the space in the head of thecharger, such that, when the prosthesis and the clip are in the head ofthe charger, the prosthesis is held firmly by the gripping means of theclip which are then compressed between the prosthesis and the internalwall of the space arranged in the head of the charger and, when theprosthesis exits from the head of the charger, it is held less firmly bythe clip, so as to be able to be released therefrom.

BRIEF DESCRIPTION OF FIGURES

Other particular features and advantages of the embodiments of presentinvention will emerge more clearly from the description hereinbelow,given in reference to the attached drawings, in which:

FIG. 1a illustrates a perspective view of a prosthesis according to anembodiment of the invention, viewed from the front.

FIG. 1b illustrates a top view of a prosthesis with the planes ofsection A-A and B-B, respectively of FIGS. 1c and 1 d,

FIG. 2a illustrates a top view of the core equipped with its protectiveshell in an embodiment of the invention, with the planes of sections A-Aand B-B, respectively of FIGS. 2b and 2 c.

FIGS. 2d and 2e illustrate, in perspective, respectively, a top view anda bottom view of the core equipped with its protective shell.

FIGS. 3a and 3b illustrate respectively a profile view and a top view inperspective of a core deprived of a protective shell in an embodiment ofthe invention.

FIGS. 3c and 3d illustrate, in perspective, respectively, a top view anda bottom view of the protective shell of the core according to anembodiment of the invention,

FIG. 4a illustrates a bottom view of the upper plate of the prosthesis,with the planes of sections A-A and B-B, respectively of FIGS. 4c and 4d.

FIG. 4b illustrates a side view of the upper plate of the intervertebraldisc prosthesis according to an embodiment of the invention,

FIG. 5a illustrates a top view of the lower plate of the prosthesis.

FIGS. 5b and 5c illustrate respectively side views and front views ofthe lower plate of the prosthesis and FIGS. 5d and 5e illustrate, inperspective, respectively, a top view and a bottom view of the lowerplate of the intervertebral disc prosthesis according to an embodimentof the invention,

FIG. 6a illustrates a view in perspective of the clip of the insertiondevice of intervertebral disc prostheses between two vertebrae.

FIGS. 6b and 6c illustrate a partial profile and top view, respectively,of the head of the charger of the prosthesis insertion device betweentwo vertebrae, with the prosthesis held by the clip in extendedposition.

FIG. 6d illustrates a view in perspective of the clip of the insertiondevice of intervertebral disc prostheses between two vertebrae.

FIG. 7a illustrates a top view of the complete prosthesis insertiondevice between two vertebrae when the prosthesis held by the clip isretracted into the head of a charger.

FIG. 7b illustrates it according to the section plan D-D of FIG. 7 a.

FIG. 7c illustrates a top view of the complete prosthesis insertiondevice between two vertebrae when the prosthesis held by the clip isextended from the head of the charger.

FIG. 7d illustrates it according to the section plan D-D of FIG. 7 c.

DESCRIPTION OF PREFERRED EMBODIMENTS

The intervertebral disc prosthesis according to an embodiment of thepresent invention is comprised of a first plate (1) articulated relativeto a second plate (2) by means of a core (3), as evident in particularin FIGS. 1a, 1c and 1d . In the following description, the first plate(1) is called the upper plate and the second plate (2) is called thelower plate, according to the orientation given to the prosthesis shownin the drawings. Those of skill will recognize after appreciating thisdisclosure that the prosthesis could be inversely oriented between thevertebrae, so that the first plate (1) would be the lower plate and thesecond plate (2) would be the upper plate. An advantage of theprosthesis according to the present invention is that it comprisessimple pieces which can be dimensioned so that the prosthesis is placedon the cervical spine.

The core (3) is of less thickness (for example 3 mm in a preferredembodiment) for a cervical prosthesis or thicker (for example 15 mm in apreferred embodiment) for a lumbar prosthesis.

In another embodiment, a part of the upper surface of the upper plate(1) is bulged, as shown in FIGS. 4b to 4d , so as to better adapt to thevertebra on which the prosthesis is intended to be placed, the lowersurface of the vertebrae being hollow. The bulged part of the upperplate (1) is then situated in the front part of the upper plate, asshown in particular in FIG. 4d . The lower plate (2) is substantiallyflat and in preferred embodiments, its lower surface has no requirementto be bulged or hollow, since the upper surface of the vertebrae issubstantially flat.

In the embodiment of FIGS. 1a to 1d, 4b to 4d and 5b to 5 e, the uppersurface of the upper plate (1) and the lower surface of the lower plate(2) are provided with teeth or notches (11, 21) situated in the regionof at least two edges of the prosthesis. These notches (11, 21),oriented so as to prevent sliding of the prosthesis, serve as anchorsfor the prosthesis at times when the osseous tissue adheres to thesesurfaces of the plates in contact with the vertebrae. In fact, theosseous tissue, in the few weeks following surgical intervention forimplanting the prosthesis, will invade the surfaces with which it is incontact. A porous biocompatible coating is provided on these surfaces toallow adhesion of the osseous tissue and its definitive fusion with theprosthesis.

In another embodiment, the lower surface of the core (3) is enclosed bya protective shell (4) of the core. This protective shell (4) is, forexample, drilled, in the centre of its lower surface, with at least onehole (41), for example a dummy, which improves sliding on the uppersurface of the lower plate (2). In a simpler variant embodiment, in theabsence of this protective shell (4), it is the lower surface of thecore (3) which, for example, will be pierced by a dummy hole in itscentre. The core alone will then have substantially the same appearanceas the ensemble made up by the core (3) and its protective shell (4),such as in the embodiment described hereinafter and illustrated in FIGS.2a to 2e . The size and form, for example oval, of the hole (41) throughthe core (3) or the protective shell (4) are adapted to the size andform of the core or of the protective shell. The hole will have beenmade so that the angles formed by its edges (411) are softened to reducefriction on the lower plate. This hole (41) of adapted dimensions can ofcourse be replaced by a plurality of smaller holes, whereof the extentwill be adapted to the size and form of the core or of the protectiveshell. For example, a multitude of concave minuscule alveoli could bearranged on the lower surface of the core or of the protective shell.

In a variant embodiment the dummy hole (41) present at least on thelower surface of the core (3) or of the protective shell (4) of the coreis prolonged by grooves (410) which extend as far as the periphery ofthis lower surface. These grooves (410) thus form channels via whichinterstitial liquid from surrounding tissue can slide between the lowersurface of the core (3) or of the protective shell (4) and play alubricating role to improve sliding of the core (3) on the upper surfaceof the lower plate (2).

The hole (41) and the eventual grooves (410) may be such that the areaof contact between the lower surface of the core (3) and the uppersurface of the lower plate (2) is substantially equal to the area ofcontact between the upper surface of the core (3) and the lower surfaceof the upper plate (1). The constraints applied to the prosthesis willthus be absorbed equally by both surfaces of the core (3) in thisembodiment, which will allow reducing frictions and improving the lifeduration of the core by optimizing the displacement of the core (3)relative to the plates (1, 2).

In the embodiment where the lower surface of the core (3) is enclosed bya protective shell (4), the lower part of the core may be narrower thanits upper part, such that once the protective shell (4) is mounted onthe lower part, the core has substantially homogeneous dimensions, asshown in FIGS. 2a to 2e . On the circumference of the core,substantially at the centre of its thickness, a groove (33), shown inFIGS. 2b, 2c and 3a , complementary to a groove (43), illustrated inFIGS. 2b, 2c and 3c , present on the internal part of the edges of theprotective shell (4), provides cohesion of the ensemble made up by thecore (3) and its protective shell (4). The core (3) will then be simplyencased in the protective shell (4) when the prosthesis is mounted.

The core (3) in this embodiment has, on at least one part of its uppersurface, a convex part (32), evident particularly in FIGS. 2a to 2d, 3aand 3b , complementary to a concave part (12) of the upper plate (1),evident particularly in FIGS. 4a, 4c and 4d . This concave part (12)permits inclination of the upper plate (1) when the patient wearing theprosthesis bends over. The lower surface of the core (3) or of theprotective shell (4) and the upper surface of the lower plate (2) couldbe plane, or substantially flat, so as to permit clearance of the core(3) relative to the lower plate (2), both in translation according to anaxis substantially parallel to the lower plate (2), and in rotationabout an axis substantially perpendicular to the lower plate (2). Duringmovements made by the patient wearing the prosthesis, this inclinationof the upper plate (1) and this clearance of the core will allowdisplacement of the core (3) towards the ideal position to absorb theconstraints applied to the prosthesis. The movement between the upperplate (1) and the core (3), as well as the clearance of the core (3)relative to the lower plate (2) thus allow the patient to move, and,optionally, to eliminate the defects of positioning the prosthesis. Thisclearance likewise has the advantage of preventing premature wear due tothe constraints applied to the prosthesis. The dummy hole (41) bored inthe lower surface of the core (3) or of the protective shell (4) willhelp improve sliding of the core on the upper surface of the lowerplate, so that the core can find the ideal position for absorbing theconstraints imposed on the prosthesis as fast and as easily as possible.For good absorption of the constraints, the core (3) could, for example,be made of polyethylene, or other materials that are compressible andmay simulate physical properties of natural intervertebral discs such aselasticity, for example.

According to an embodiment of the invention, the lower surface of a core(3) made of compressible material could be enclosed by a metallicprotective shell (4), permitting better sliding on the lower metallicplate (2) and reduction in creep of the compressible material. Thesliding of the core will be improved by a hole (41), for example adummy, bored in the lower surface of the protective shell (4).

In the embodiment of FIGS. 1a, 1c and 5a to 5e the lower plate (2)comprises two contact plates (22) situated opposite one another on twoedges of the lower plate (2), at each lateral sides of the lower plate(2). Each contact plate (22) comprises male structure of the lower plate(2) and can penetrate female structure of the core, constituted in thisembodiment by a recess (31) of the core (3) on two of its edges. In theembodiment shown in these figures, the dimensions of each recess (31) ofthe core (3) are slightly greater than those of each nib (22) of thelower plate (2) so as to limit clearance of the core (3) relative to thelower plate (2), both in translation along an axis substantiallyparallel to the lower plate (2), and in rotation about an axissubstantially perpendicular to the lower plate (2).

In the embodiment where a core (3) made of compressible material isprovided with a protective metallic shell (4) sliding on a lowermetallic plate, the protective shell could be in an adapted form so thatit is not in contact with a metallic limit stop of the lower plate. Sucha result can be obtained, for example, thanks to the fact that the edgesof the protective shell (4) are slightly offset from the limit stops ofthe core. This variant embodiment can prove necessary since, in a livingorganism, it is preferable to avoid the shocks between two metallicmaterials, which risk projecting metallic particles into the surroundingtissue and causing complications.

In a variant embodiment not shown, the dimensions of each recess (31) ofthe core (3) are substantially the same as those of each nib (22) of thelower plate (2), so as to avoid any clearance of the core (3) relativeto the lower plate (2), both in translation and in rotation. In thelatter case, the only permitted movement of the prosthesis is that ofthe upper plate (1) relative to the core (3).

In a variant embodiment not shown, the contact plates (22) are replacedby nibs curved towards the interior of the prosthesis, above the edgesof the core (3), so as to prevent the core from being raised. In anothervariant, one of the nibs is replaced by a contact plate (or pin)equipped with a hole in which, for example, a dowel fixes a plate (orhasp). The ensemble made up by the hasp fixed on the contact plate willhave the same form as the nib of the opposite side and will fulfil thesame function with the added advantage of facilitating mounting of thedifferent pieces of the prosthesis. In a variant embodiment, the twonibs are each replaced by a contact plate to which a hasp is fixed.

In another variant embodiment not shown, the contact plates (22) of thelower plate (2) are replaced by half dog points. The core (3), by way ofcomplement, does not comprise recesses (31), but two wells under itslower surface. The dimensions of the half dog points of the lower plate(2) and of the wells of the core (3) will be adapted according to thedesired result, by choice, of slight clearance of the core intranslation and in rotation or any clearance.

In another embodiment not shown, the contact plates (22) of the lowerplate (2) are replaced by walls, positioned opposite one another, in thevicinity of two substantially parallel edges of the lower plate, butmore towards the interior of the prosthesis than the contact plates(22). The core (3) comprises recesses complementary to the walls. Thedimensions of each recess of the core of this embodiment are, eitherslightly greater, or substantially the same as those of each wall of thelower plate, so as to allow or not slight clearance in translation andin rotation.

In yet another embodiment not shown, the female cooperation means aresituated on the lower plate (2) and the male cooperation means on thecore (3).

An intervertebral disc prosthesis according to many embodiments of thepresent invention help to correct the defects of lordosis. The presenceof an acute angle, for example of between 0° and 15° , in thepostero-anterior direction, between the upper plate (1) and the lowerplate (2) of the prosthesis could be desired. To adjust the anglenecessary as a function of the patient, it suffices to select a core (3)with an appropriate angle between the average plane representing itsupper surface and the plane passing through its lower surface. Such anangle could likewise be obtained by making an upper plate, including theplane means representing its lower and upper surfaces forming an angle.Another possibility involves the lower plate whereof the plane meansrepresenting its lower and upper surfaces form an angle. Anotherpossibility consists of a position of the core slightly offset to therear or the front relative to the centre of the prosthesis including theplates which will then form an angle. This slightly offset position ofthe core can, for example, be maintained due to adjustable positioningof the male and female limit stops.

In the event where the male structure or stop in the vicinity of theedges of the core (i.e., near the periphery of the core) and the femalestructure or stops are situated in the vicinity of the edges of thelower plate (i.e., near the periphery of the lower plate), a lordosiscore (by the fact that if forms an acute angle in the postero-anteriordirection) can then be made solid with the plate by a projectionpenetrating a cavity or opening in the lower plate. If the surgeon wantslordosis determined for a patient, he will select a core (3) whichcannot have any clearance relative to the lower plate (2). However, ifhe only wants the lordosis to remain within a range of values, he willselect a core which can have slight clearance in translation and inrotation relative to the lower plate (2), but about a position imposingslight permanent inclination of at least one of the plates.

The intervertebral disc prosthesis according to a variety of embodimentsof the present invention can, in variant embodiments, be anchoredsolidly, from when implanted, in the vertebral column to prevent theprosthesis from migrating under the effect of the resulting transversalof the force exerted by the vertebral column on the prosthesis in place,an important consideration in lordosis. In this case, the lower plate(2) comprises one or more openings situated in the vicinity of the rearside of the prosthesis, receiving anchors of a variety of types.

Therefore, in a variant embodiment, the openings in the lower plate (2)are circular and the anchors preferably have the shape of studs, with ahead having a size greater than that of the openings to allow the lowerplate (2) to be sandwiched between the head of the anchors and thevertebra on which the prosthesis is anchored. For greater security, theopenings could be made such that the anchors and the lower plate form anangle of less than or equal to 90° .

Intervertebral disc prostheses are typically not easy to implant in thepatient. This difficulty is exacerbated by the fact of the relativemobility of the pieces of the prostheses. It is thus preferred toassociate these prostheses with a device allowing it to be held andinserted between the vertebrae. Such a device according to an embodimentof the present invention is made up of a clip (7) whereof the frontsurface (71) has a shape provided to fit the form of the front edge ofthe prosthesis. This clip (7) has a fitting on its front that grips (72)the prosthesis. These gripping means (72) can, for example, be two (72)flexible blades mounted on the lateral edges of the clip and can holdthe prosthesis by pinching the lateral edges of the upper and lowerplates of the prosthesis. The front surface (71) of the clip (7) haspreferably, for example, a height at least substantially equal to theheight of the prosthesis, so as to come into contact with the frontedges of each of the plates of the prosthesis.

In an embodiment of the invention, a groove (711) is present in themedian part of the front surface (71) of the clip (7) so as to come intocontact with the front edge of the core, slightly set back relative tothe front edges of the plates. There can of course be several groovesfitting the shape of the prosthesis. The front surface (71) of the clip(7) provided with the groove (711) thus fits the form of the front edgeof the prosthesis when in contact with the three elements making up theprosthesis. The clip thus helps hold the prosthesis and push ithomogeneously towards its opening between two vertebrae. This clip (7)is provided to hold the prosthesis and to be inserted into a charger (6)(or loader). This charger (6) has a head (62) in which a space isarranged to receive the clip holding the prosthesis and a body (61)provided to slide about a rod, called a guide (5). The rear surface ofthe clip (7) can be provided with a hole in its centre, provided toinsert an end (54) of the guide (5) so that the guide (5) can hold andpush the clip (7). The guide (5) is equipped with a pusher (52) at itsother end, which will help push the clip and the prosthesis out of thehead (62) of the charger (6) by having the guide (5) slide in the body(61) of the charger (6). An adjustable stop is mounted on the guide (5).For example, a threaded ring (53) is screwed around the guide. This ringserves as a stop (53) to the guide when it slides in the body (61) ofthe charger (6). The position of the stop (53) will be adjusted, as afunction of the size of the vertebra, so that when the stop (53) of theguide (5) comes into contact with the body (61) of the charger (6), theend (54) of the guide (5) will have pushed the clip (7) as far as aposition where the prosthesis, held by the flexible blades (72) of theclip, is now out of the head (62) of the charger (6) and centredrelative to the axis of the vertebral column.

In an embodiment of the prosthesis according to the invention, asdescribed earlier, the upper (1) and lower (2) plates are provided withanchors as such teeth or notches (11 and 21) for example, on theirsurface in contact with the vertebrae. These anchors or notches (11, 21)are oriented so as to oppose displacement of the prosthesis in thedirection of withdrawal of the clip (7), once the prosthesis is enteredin its opening between two vertebrae, made in advance by the surgeon.These notches (11, 21) are thus oriented so as to allow the prosthesisto return to its opening but not come out when the surgeon pulls backthe clip (7) holding the prosthesis. On the other hand, the front end ofthe gripping means (72) of the prosthesis is larger (thicker) than theirback end. The width of the clip at its back end is substantially equalto (or slightly smaller than) the width of the space in the head (62) ofthe charger (6). Thanks to these substantially equal dimensions of thespace inside the head (62) of the charger (6) and of the prosthesis andthe clip (7), when both the latter are in the head (62) of the charger(6), the prosthesis is solidly held by the flexible blades (72) of theclip (7) whereof the front ends are compressed between the prosthesisand the internal wall of the space made in the head (62) of the charger(6). When the surgeon presses on or strikes the pusher (52) of theguide, the prosthesis exits from the head (62) of the charger and it isheld less firmly by the clip (7) since the back ends of the flexibleblades (72) are less compressed than were the front ends. The prosthesiscould then be released from the clip by pulling back the insertiondevice, owing to the presence of the notches on the lower and upperplates, allowing the prosthesis to remain in its opening between the twovertebrae.

The present invention allows embodiments in numerous other specificforms without departing from the spirit of the invention. As aconsequence, the present embodiments must be considered by way ofillustration only, and can be modified within the scope defined by therange of the attached claims, and thus, the invention should be.

Although the present invention has been described in detail, it will beapparent to those skilled in the art that many embodiments taking avariety of specific forms and reflecting changes, substitutions andalterations can be made without departing from the spirit and scope ofthe invention. Therefore, the described embodiments illustrate but donot restrict the scope of the claims.

1. An intervertebral disc prosthesis comprising: a plate comprising asubstantially flat surface; and a core comprising a substantially flatsurface configured for sliding movement along the substantially flatsurface of the plate, and a dummy hole disposed in the substantiallyflat surface of the core.
 2. The intervertebral disc prosthesis of claim1 in which the substantially flat surface of the core is formed in aprotective shell attachable to an upper portion of the core.
 3. Theintervertebral disc prosthesis of claim 1 in which the protective shellof the core is made of metal.
 4. The intervertebral disc prosthesis ofclaim 1 in which the substantially flat surface of the core comprises achannel.
 5. The intervertebral disc prosthesis of claim 1 in which thechannel is a groove.
 6. The intervertebral disc prosthesis of claim 6 inwhich the core comprises plural grooves intersecting at the dummy hole.7. The intervertebral disc prosthesis of claim 1 in which thesubstantially flat surface of the core comprises plural channels, eachextending along the substantially flat surface of the core radially fromthe dummy hole.
 8. A system for treatment of a spine comprising: anintervertebral prosthesis; and an instrument for insertion of theintervertebral prostheses comprising a rod, a charger comprising a headhaving an internal space comprising laterally opposed walls and apassage for the rod, and a clip comprising laterally opposed blades anda hole configured to receive an end of the rod; the system having anintervertebral prosthesis insertion configuration in which theprosthesis is disposed between the laterally opposed blades, the clip iswithdrawn in the head with each of the laterally opposed walls incontact with a respective one of the laterally opposed blades, and theend of the rod is disposed in the hole, and an instrument withdrawalconfiguration in which the intervertebral prosthesis is extended outsidethe head with the intervertebral prosthesis releasably retained by thethe laterally opposed blades.
 9. The system of claim 8 in which thefront surface of the clip comprises a form configured to fit the form ofan edge of the prosthesis.
 10. The system of claim 8 in which the rodcomprises a stop adjustably configurable to define a maximum extensionof the clip out of the head with the system in the instrument withdrawalconfiguration.
 11. The system of claim 8 in which the laterally opposedwalls compress the laterally opposed blades against the intervertebralprosthesis with the system in the intervertebral prosthesis insertionconfiguration.
 12. A of treating a spine comprising the steps of:acquiring an intervertebral prosthesis and an instrument comprising arod, a charger comprising a head having an internal space comprisinglaterally opposed walls and a passage for the rod, and a clip comprisinglaterally opposed blades and a hole configured to receive an end of therod; placing the clip on the end of the rod with the end of the roddisposed in the hole; placing the intervertebral prosthesis between thelaterally opposed blades; gripping the intervertebral prosthesis in thehead by placing the laterally opposed blades along the laterally opposedwalls with the intervertebral prosthesis compressed by the laterallyopposed blades; pushing the rod to advance the clip and intervertebralprosthesis out of the head and into a space between adjacent vertebrae;and removing the intervertebral prosthesis from the clip by pulling therod away from the space.